Pelletizing process

ABSTRACT

A method of making pellets is provided. The method may include grinding a biomass to a smaller particle size, forming a ground biomass. The ground biomass may then be placed within a conditioner and steamed for more than about 20 seconds, forming a steamed and ground biomass. The steamed and ground biomass may be formed into a plurality of pellets using a die having a larger open area.

BACKGROUND OF THE INVENTION

The present invention relates to a pelletizing method and, more particularly, to a pelletizing process with improved conditioning.

Pelletizing is the process of compressing or molding a material into the shape of a pellet. A wide range of different materials are pelletized including chemicals, iron ore, animal compound feed, wood and more.

Pellet fuels are heating fuels made from compressed biomass. Wood pellets are the most common type. A form of wood fuel, wood pellets are generally made from compacted sawdust or other wastes from sawmilling and other wood products manufacture.

Pellets are manufactured in several types and grades as fuels for electric power plants, homes, and other applications in between. Pellets are extremely dense and can be produced with a low moisture content (below 10%) that allows them to be burned with a very high combustion efficiency.

With the surge in the price of fossil fuels since 2005, the demand for pellet heating has increased in Europe and North America, and a sizable industry is emerging.

As can be seen, there is a need for an improved and more efficient pelletizing process.

SUMMARY OF THE INVENTION

In one aspect of the present invention, a method of forming pellets comprises: grinding a biomass to a smaller particle size forming a ground biomass; steaming the ground biomass in a conditioner for more than about 20 seconds forming a steamed and ground biomass; and pelletizing the steamed and ground biomass forming a plurality of pellets.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a flow chart of an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is of the best currently contemplated modes of carrying out exemplary embodiments of the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims.

Pellets are produced by compressing the wood material which has first passed through a hammer mill to provide a uniform dough-like biomass. The biomass of the present invention is then steamed for a certain period of time. This biomass is fed to a press where it is squeezed through a die having holes. The high pressure of the press causes the temperature of the wood to increase greatly, and the lignin plasticizes slightly forming a natural glue that holds the pellet together as it cools.

Referring to the FIGURES, the present invention may include a method of making pellets. The method may include first grinding a biomass to a smaller particle size, forming a ground biomass 100. The ground biomass may then be placed within a conditioner and steamed for more than about 20 seconds, forming a steamed and ground biomass 200. The steamed and ground biomass may be formed into a plurality of pellets using a die having a larger open area 300.

As mentioned above, the present invention includes the process of grinding a biomass into a smaller particle size forming a ground biomass. The biomass of the present invention may include woody material, grass and the like. A grinding hammer mill may be used to grind the biomass of the present invention. The hammer mill may include a delivery device for intake, and plurality of hammers and rods for grinding the biomass. The ground biomass may filter through a screen. Various screen sizes may be used to grind the biomass into various particle sizes.

In certain embodiments, the biomass may be ground to a particle size of about 4 mm up to about 8 mm, from about 5 mm up to about 7 mm, or about 6 mm, depending on the screen size. In certain embodiments, the screen size selection is determined by the incoming biomass size. For example, if the biomass is ⅝inch or less prior to grinding, the screen may include apertures from about 4 mm up to about 5 mm. The small size of the ground biomass increases the surface area. The ground biomass may weigh about 10-11 lbs per cubic feet and may include around 7% up to about 11% moisture.

Once the biomass has been ground, the ground biomass is conditioned. The conditioning of the ground biomass may include steaming the ground biomass within a conditioner. A boiler may be used to produce the steam. The steam may be delivered at a PSI of about 15 to about 30, which may raise the temperature of the biomass from ambient up to about 150° F. to about 180° F. In certain embodiments, the steam may be supplied at a rate of about 450 lbs of steam per ton of pellet production.

The ground biomass may retain within the steam for a certain period of time. In certain embodiments, the ground biomass may be retained within the steam from about 20 seconds up to about 2 minutes, for about 45 seconds up to about 100 seconds, or for about 1 minute. As mentioned above, the temperature may reach 150° F. and above during the retention time. After the conditioning step, the steamed and ground biomass may have a density of about 3 to about 4 pounds per cubic feet, which increases the production rate of the pellets.

Once the biomass has been ground and conditioned, the pellets are formed by pelletizing. A roller is used to compress the biomass against a heated metal plate called a die. The die includes several small holes, which allow the biomass to be squeezed through under high temperature and pressure conditions. If the conditions are right, the biomass particles will fuse into a solid mass, thus turning into a pellet. The die may include an open area, which is calculated by the amount of holes that are through the die. The use of steam and improved conditioning reduces the stress undertaken by the die, which allows the use of dies that include a higher open area. For example, the open area may range from about 35% to about 50% of the die. The wood pellet formed may include a minimum bulk density after compression of about 40 lbs/cuft. It should be understood, of course, that the foregoing relates to exemplary embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims. 

What is claimed is:
 1. A method of forming pellets comprising: grinding a biomass to a smaller particle size forming a ground biomass; steaming the ground biomass in a conditioner for more than about 20 seconds forming a steamed and ground biomass; and pelletizing the steamed and ground biomass forming a plurality of pellets.
 2. The method of claim 1, wherein the biomass is ground to a particle size of about 4 mm to about 8 mm.
 3. The method of claim 1, wherein the biomass is ground to a particle size of about 5 mm to about 7 mm.
 4. The method of claim 1, wherein the biomass is ground to a particle size of 6 mm.
 5. The method of claim 1, wherein the biomass comprises a woody material.
 6. The method of claim 1, wherein the steam is delivered at a pressure of about 15 PSI to about 30 PSI.
 7. The method of claim 1, wherein the steaming raises the temperature of the biomass to about 150° F. and up to about 180° F.
 8. The method of claim 1, wherein the steaming of the ground biomass is for about 20 seconds and up to about 2 minutes.
 9. The method of claim 1, wherein the steaming of the ground biomass is for about 45 seconds and up to about 100 seconds.
 10. The method of claim 1, wherein the steaming of the ground biomass is for about 1 minute.
 11. The method of claim 1, wherein the steamed and ground biomass has a density of about 3 to about 4 pounds per cubic feet.
 12. The method of claim 1, wherein pelletizing the steamed and ground biomass comprises the step of compressing the steamed and ground biomass against a die comprising a plurality of openings forming an open area.
 13. The method of claim 12, wherein the open area ranges from about 35% to about 50% of the die.
 14. The method of claim 1, wherein the plurality of pellets each comprise a minimum bulk density of 40 lbs/cuft. 